https://gcc.gnu.org/bugzilla/show_bug.cgi?id=64867
--- Comment #5 from Tom Tromey <tromey at gcc dot gnu.org> --- (In reply to Jason Merrill from comment #3) > Passing a non-POD to a varargs function is conditionally-supported, with > implementation-defined semantics. In GCC 5 it's supported and treated like > normal pass-by-value. You can get a diagnostic about it with > -Wconditionally-supported. I tried this today and it does not work with the test case in comment #4. pokyo. gcc --version gcc (GCC) 5.0.0 20150129 (experimental) Copyright (C) 2015 Free Software Foundation, Inc. This is free software; see the source for copying conditions. There is NO warranty; not even for MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. pokyo. g++ --std=c++11 --syntax-only -Wall -Wconditionally-supported q.cc pokyo.